What it is:

I was typing in a sign i had and deleted all of it other than empty lines and first it showed ## empty }} and a few days later i reproduced it on a different sign about 200 blocks away and it showed {{ empty }}.

How to reproduce:

Place down a sign on the ground and press the 'Enter' button twice. Type in 'empty' (No apostrophes) and backspace it without deleting any lines. The word '{{ empty }}' should appear, or something similar to it. NOTE THIS WAS ON AN OLD WORLD REALM ON BEDROCK.